This invention relates to food preparation ovens and more particularly to food preparation ovens for preparing pizza and similar types of food products. Specifically the invention relates to an impingement oven wherein food products are baked or cooked by means of jets of hot gaseous fluid such as hot air and wherein the hot air jets are impinged directly upon localized areas of the food product.
In the fast food restaurant business, it is important that food be prepared very quickly and that the amount of kitchen space required for food preparation is minimized so that productivity per square foot of kitchen floor space is maximized. Due to the ever increasing competitiveness of the fast food business, restaurants need to be able to serve dinners ever more quickly thus requiring that food preparation time be reduced. Restaurants seek to be able to serve more customers without adding additional space in seating areas.
Quick preparation of food is especially important for those restaurants which serve pizza since it takes longer to prepare. One of the reasons that preparation time for pizzas is longer than for other fast foods is the nature of the pizza product. As opposed to other types of fast foods which primarily consist of meat products such as beef, chicken, or fish, all of which can be prepared rather quickly by grill frying or deep fat frying, pizza consists of a combination of a dough shell and a variety of toppings such as various types of cheeses, meats, and vegetables, i.e., onions, mushrooms, green peppers and the like, all of which must be adequately cooked rather than deep fried and which, therefore, require special handling. It is thus more difficult to cook a pizza and similar food products very quickly as opposed to preparing items such as hot dogs, hamburgers, fried chicken, and the like.
To increase the speed in which pizzas are prepared, it is not sufficient to merely increase the temperature of the oven in which the pizza is cooked. An increase in temperature could result in breakdown of the components of the pizza, and could possibly result in burning the pizza.
Advances have been made in the speed at which pizzas may be prepared by providing impingement ovens wherein a conveyor transports food products through an oven cavity. U.S. Pat. Nos. 4,701,340, and 4,626,661, both of which are assigned to the assignee of the present invention and are incorporated herein by reference, disclose impingement ovens which have been commercially very successful.
In conventional impingement ovens, the air, after its distribution through the plenum and the impingement finger ducts, goes back to the fan by way of the top, bottom and sides of the oven. Some of the air escapes through openings in the side walls of the oven through which the conveyor extends thereby resulting in lost energy and reducing the efficiency of the oven. It is therefore desired to provide an impingement oven wherein the heated air being recirculated to the fan is maximized, and the amount of cool air entering the fan from the conveyor openings is minimized.
Axial fans are conventionally used with impingement ovens because of their superior air movement characteristics since they provide high velocity, low pressure air flow. The height of prior art impingement ovens has been dictated by the size of the axial fans which have been used with such ovens. Therefore, one approach to reducing oven height is to use multiple axial fans, whereby each fan would have a smaller diameter than the single fan which is used with prior art impingement ovens. An impingement oven of reduced height allows a greater number of ovens to be stacked upon one another to increase the productivity of the kitchen floor space without sacrificing food preparation time or food quality. However, a problem with using multiple axial fans in impingement ovens is that the fans tend to set up lateral air flow across the oven cavity, thereby starving one of the fans of return air. Another problem is that a helical air flow effect may be set up in the plenum, thereby creating uneven pressures in the impingement finger ducts and causing an uneven supply of thermal energy to the food product. It is, therefore, desired to provide an impingement food preparation oven having multiple axial fans in which an even air flow distribution is obtained from each plenum into the finger ducts.
As indicated, impingement ovens recirculate air by means of a fan and plenum assembly for reheating impinging air in the cooking process. Generally, the fan withdraws air from the cooking area and recirculates it over a heat source from which it is drawn and directed into a plenum for distribution to various finger ducts, which direct the air to the product to be cooked. A prerequisite for an evenly cooked food product is the uniform distribution of reheated air through impinging nozzles located along each finger duct. A problem with conventional impingement ovens is that the air traveling through the finger ducts tends to remain therein and exits through the nozzles furthest from the plenum. As a result, a nonuniform impingement occurs with greater heating taking place at points furthest from the plenum along each finger duct. Therefore, it is desired to provide an impingement oven in which the impinging jets of air are uniformly distributed through each nozzle on the finger duct.
Another problem with conventional impingement ovens is the effect of escaping air on the oven control circuitry, which controls and monitors the oven during the cooking process. For example, most oven control boxes containing oven control circuitry are mounted directly on, or in close proximity to, the oven, and if this environment becomes too warm due to escaping radiating heat from the cooking chamber, the oven circuitry may provide improper operation or monitoring of the cooking process, or even prematurely fail. Naturally, the occurrence of either of these two situations is highly undesirable since either will result in an improperly cooked food product and expensive maintenance.
The above problem is particularly compounded in a multiple stacked food preparation oven arrangement wherein the upwardly radiating heat from the lowermost oven contacts and heats the oven control circuitry or the mounting surfaces on which the circuitry is disposed. The two primary sources of this escaping radiating air are generally the cooking chamber and the conveyor device extending through the horizontally disposed oven passageway for conveying cooked food products from the cooking chamber. Another source of escaping radiating heat can be the oven plenum, however, this potential source is generally of secondary importance since it is usually disposed near the back of the oven, while the oven control circuitry is generally disposed near the front of the oven. In a multiple stacked food preparation oven arrangement, the close proximity of the uppermost oven control circuitry and mounting surfaces to the lowermost oven subjects the circuitry and mounting surfaces to a much hotter environment than if the ovens were situated side by side, thereby requiring a great amount of forced cooling air to lower the temperature of the control circuitry environment.
Attempts to prevent the overheating of the oven control circuitry or the mounting surfaces on which the circuitry is disposed, include directing forced air against the circuitry and the mounting surfaces to cool them from the upward radiating heat of the lowermost oven. One solution that has worked well in cooling the oven control circuitry is described in U.S. Pat. No. 4,539,469, which is assigned to the assignee of the present invention. This patent discloses the use of a double wall assembly having a mounting wall on which the oven circuitry is disposed and an exterior wall spaced apart from the mounting wall. The mounting wall and the exterior wall form therebetween a ventilating compartment. Thus, the double wall assembly provides a continuous flow of cooling air between the mounting wall and exterior wall to insulate the oven control circuitry from the high temperatures of radiating heat. This double wall assembly has performed effectively to cool the oven control circuitry.
Notwithstanding this successful performance, efforts are continuously directed toward increasing the efficiency of the cooling process. In U.S. Pat. No. 4,539,469, the inlet of the ventilating compartment is located on the back wall of each oven. Thus, the cooling air entering the uppermost ovens is warmer than the cooling air entering the bottom oven near the floor. It is thus desired to provide the same cooling air that enters the bottom of the oven to the uppermost ovens.